1. Field of the Invention
The present invention relates to a polymer scale preventive agent for use in polymerization of a monomer having an ethylenically unsaturated double bond, a polymerization vessel wherein polymer scale is effectively prevented from being deposited, and a process of producing a polymer using the same.
2. Description of the Prior Art
Hitherto, as processes of polymerizing a monomer having an ethylenically unsaturated double bond, for example, the suspension polymerization, the emulsion polymerization, the solution polymerization, the gas phase polymerization, and the bulk polymerization are known. In any of these processes, polymer scale is apt to be deposited at parts where the monomer comes in contact, for example, on the inner wall surface of a polymerization vessel and an agitator.
If polymer scale is deposited, for example, the yield of the polymer drops, the capacity of cooling the polymerization vessel decreases, and further the poller scale is peeled off and is mixed with the polymer, thereby disadvantageously degrading the item that is obtained by molding the polymer. In addition, to remove the deposited polymer scale, not only too much labor and time are required but also since the polymer scale contains unreacted monomer, there is a danger that the human body will be injured by that monomer, which has become quite a serious problem in recent years.
Concerning prevention of deposition of polymer scale on the polymerization vessel inner wall surface and the like as mentioned above, conventionally, a method wherein a polymer scale preventive agent comprising a polar organic compound such as an amine compound, a quinone compound, and an aldehyde compound is applied and a method wherein such a polar organic compound is added to an aqueous medium are known (Japanese Patent Publication (kokoku) No. 45-30343 (1970)), which are used, for example, in some cases of suspension polymerization of vinyl chloride.
However, although these methods exhibit an effect of preventing polymer scale from being deposited until the polymerization is repeated to the extent of about 5 to 6 batches, when the polymerization is repeated further, the preventive effect declines (i.e., the preventive effect is poor in durability), which is a disadvantage. In this regard, the influence is particularly serious where an water-soluble catalyst is used, and these methods are not satisfactory from an industrial point of view.
In order to overcome this disadvantage, Japanese Pre-examination Patent Publication (kokai) No.53-13689 (1978) suggests the use of a condensation product of an aromatic amine compound as a polymer scale preventive agent. If a coating film containing this condensation product of an aromatic amine compound is formed on the part where a monomer comes in contact such as the polymerization vessel inner wall surface or the like, polymer scale is not deposited on the liquid phase part in the polymerization vessel even if the polymerization is repeated to the extent of 100 to 200 batches. Further, even in the case where a water-soluble catalyst is used, similarly polymer scale is prevented from being deposited on the liquid phase part,
However, there is a defect that polymer scale is deposited near the interface between the gas phase part and the liquid phase part positioned at the upper part of the polymerization vessel.
Once polymer scale is deposited near the interface between the gas phase part and the liquid phase part, along with the repetition of the polymerization the deposited polymer scale gradually grows, ultimately leading to peeling-off of the polymer scale, which mixes into the polymer in some cases. If the polymer scale thus mixes into the polymer, where the polymer is worked into a molded item such as a sheet, many fish eyes occur in the obtained molded item, thereby degrading the molded item conspicuously.
In forming a coating film of the condensation product of an aromatic amine compound mentioned above, since the condensation product is used in the form of a coating liquid wherein the condensation product is dissolved in an organic solvent or a mixed solvent made up of an organic solvent as a major component and water (generally the content of the organic solvent is 60 wt. % or more), there is such a risk that the organic solvent will catch fire and explode, and further there is a safety problem including toxicity and the like in handling.